That's a generalization with some truth, but in this case it was blatantly obvious that iRobot was not putting much effort into improvement - or was not effective at improvement. They basically ignored the moat and relied on their headstart to the point that even brand new entrants to the market could equal or overtake them in an initial product offering.

And the business model aspects they relied on for their protective moat - e.g. mass commercial electronic production - was generalized and massively optimized in China (not just for vacuum robots but mass commercial electronics).